I should study the adsorption of a drug substance in the plastic packaging material. I have extracted the plastic by dichloromethane followed by methanol (Soxhlet extraction). After evaporation of the solvents I dissolved the remained extract in methanol and/or mobile phase, but the obtained recovery for a water soluble substance was bad.
Is there any official extraction method for the interaction study between solutions and plastic packaging material??
Thank You

Maybe the water-soluble substance was not adsorbed in the packaging material?

After the Soxhlet extraction with dichloromethan and methanol the remained plastic extract could not be dissolved with the solvent which is used in the HPLC mobile phase (methanol, acetonitril).
I could measured some amount of water soluble substance from the plastic, but the recovery from the spiked samples was only 10-20%.

Sounds like you partially dissolved your plastic (or something out of it).
How did you spike your adsorption?
See also the chain above on "Choice of optimum extraction solvents".

I would predict that the DCM/methanol soluble extract of a plastic would be composed of a number of very non-polar materials and would not be appreciably soluble in methanol or acetonitrile. Why extract the plastic in DCM/methanol if you are looking for water soluble substances? Why not use water, or water/methanol, or water/acetonitrile? But since you already have a non-polar extract, what about partitioning it between DCM or ether and water to remove most of the nonpolars, and analyse the water solubles portion?

I have obtained the description of the method (DCM/MeOH extract, dissolved in mobile phase, which contains only 15% acetonitril), but I have got only 10-20% recovery. My main question: Is there any official extraction method for the interaction study between solutions and plastic packaging material??
Thanks

The link below will get you to an application note using Accelerated Solvent Extraction (ASE). http://www.dionex.com/servletwl1/FileDownloader/slot114/77797/AN331releasedJC120400.pdf Although this method doesn't specifically deal with water-soluble additives, it does have some details that will give you the general idea as to how to proceed even if you want to use Soxhlet extraction. The main point is: don't use a solvent that can dissolve the polymer (the method cited uses IPA) and grind the polymer up using a liquid nitrogen cooled grinder in order to improve extraction efficiency. Of course, using ASE will further improve extraction efficiency and allow the extraction to be done far more rapidly.

Dear Chris,
Many thanks for the very useful informations!!!